Name: ___________________________________________________________

LIGHT

Light is an important form of energy. It can come from many sources, such as lamps, candles, or flashlights. However, our most important source of light is the sun. Without sunlight, no life would exist on Earth. Plants would be unable to make their own food and grow, so they would die. Without plants, all animals and humans would die too.

There are many different kinds of light. Frequency and wavelength determine whether or not light can be seen and what it looks like when it is seen. (Remember that frequency refers to the number of waves that pass a point in one second. Wavelength refers to the distance between the crests or troughs of the waves.)

The light we are able to see is called visible light. There are other types of light energy that are invisible to us, such as radio waves, microwaves, and x-rays. The diagram below shows all the different types of light, visible and invisible. It is called the electromagnetic spectrum.

Longest wavelength ROY – G – BIV shortest wavelength

The electromagnetic spectrum is a chart that shows many different types of energy arranged according to their wavelength.

There are many kinds of electromagnetic waves. Each kind vibrates at a different wavelength and frequency. As you go from left to right on the spectrum shown above, the wavelength decreases and the frequency increases. Some waves, such as x-rays and ultraviolet rays from the sun, are very short. Other types of electromagnetic waves include gamma waves, infrared waves, light waves, and microwaves. The only electromagnetic waves we can see are light or visible waves.

Shorter, high-energy waves such as x-rays can be harmful to people if used improperly. However, when used correctly and in short exposure times, these rays can improve and even save lives. For example, gamma rays from radioactive cobalt are used to kill cancer cells. Doctors use x-rays to “photograph” parts of the body such as teeth and potentially broken bones. Ultraviolet rays have been used to sterilize objects and kill certain kinds of bacteria.

Complete the following sentences by circling the correct phase.

1. The waves shown on the electromagnetic spectrum vibrate ( at one speed / at different speeds )

2. The waves shown on the right of the electromagnetic spectrum above vibrate

( more quickly / more slowly ) than the waves on the left.

3. In each pair below, circle the waves that vibrate faster.

a. gamma rays or radio waves

b. infrared rays or ultraviolet rays

c. ultraviolet rays or x-rays

d. visible light or radio waves

4. List the colors of the visible spectrum according to the wavelength from longest to shortest.

________________________________________________________________________________

________________________________________________________________________________

White light, such as the light we see from the sun, appears to be colorless. However, white light is actually a combination of many colors. We can see these colors when light enters a prism and spreads out. A prism is a solid (often made of glass) that bends light. We can also see these colors in a rainbow. When raindrops bend the light from the sun, the colors of the rainbow become visible. The range of colors is called the visible spectrum. The colors in the spectrum are red, orange, yellow, green, blue, indigo, and violet. Wavelength increases from one end of the spectrum to the other. The shortest wavelengths in the visible spectrum are violet. The longest ones are red.

Questions 5-10: Write T for True or F for False after each statement

5. _______All light is visible.

6. _______The color violet has the shortest wavelength of all the colors in the visible spectrum.

7. _______White light is a combination of colors.

8. _______Six colors make up the visible spectrum.

9. _______ When a rainbow forms, raindrops act much like a prism

10. _______Indigo has the longest wavelength of any color in the visible spectrum.

What happens when LIGHT strikes Matter?· 5 Things Can Happen: STARR

· S: Scattered

· T: Transmitted

· A: Absorbed

· R: Reflected

· R: Refracted

Light Can Be Absorbed· Light passes through a substance and stays there· Example: When light hits a red stop sign, the stop sign reflects mostly red wavelengths and absorbs all other colors so we do not see themLight Can Be Reflected· Light strikes a substance and bounces back· Example: When light hits a red stop sign, the stop sign reflects mostly red wavelengths and absorbs all other colors so we do not see them

The Colors of a Rainbow

Have you noticed that often when it rains and the sun is out a rainbow appears? That’s because a rainbow forms when water droplets bend the white light of the sun and it spreads out, showing the colors that make up white light. The range of colors that makes up white light is called the visible spectrum.

The name ROYGBIV can help you remember the colors of the visible spectrum in order because the name is made-up of the first letters of the colors. (Red, Orange, Yellow, Green, Blue, Indigo, and Violet) Remember that light travels in waves. Each color has a different wavelength. Wavelength increases from one end of the visible spectrum to the other. Violet has the shortest wavelength. Red has the longest.

The colors that make up white light are not only seen in rainbows. They can also be seen through the use of a prism, a wedge-shaped piece of glass. A prism bends white light as it passes through, displaying all the colors of the spectrum. Each color is bent at a different angle. Red is bent the least, while violet is bent the most.

We see different colors because items absorb and reflect different colors. Green grass, for example, reflects green light and absorbs all the other colors of the spectrum (ROYBIV).

Objects that are white reflect all the colors of the spectrum (ROYGBIV) and do NOT absorb any of them. Objects that are black absorb all of the colors of the spectrum (ROYGBIV) and do NOT reflect any of them. Think about how it feels to wear a white shirt in the hot sun and how it feels to wear a black shirt in the hot sun. You would feel warmer in the black shirt because it absorbs the sunlight. You would feel cooler in the white shirt because it reflects the sunlight.

Can You See It?

When moving light bumps into an object, the light either enters the object or bounces off. How light behaves when it hits and object depends on the material the light hits. Transparent materials, such as glass windows, allow light to pass through them with little or no interference. We can see clearly through transparent materials. Translucent materials allow light to pass through, but the light is spread out. As a result, objects behind translucent materials cannot be seen in clear detail. A frosted shower door is an example of a translucent material. Opaque materials stop the passage of light, so we cannot see through opaque objects. Examples of opaque materials are a wooden door or a steel pole. When an opaque item gets in the path of bright light, a shadow will form.

Light Can Be Transmitted· Light passes through the substance it strikes· Transparent – light passes through so you can see clearly – like window· Translucent – Light passes through but it is scattered so you cannot see clearly – like wax paper· Opaque – Light does not pass through – like construction paper

Label each object below as opaque, translucent, or transparent.

1. _________________________ a thin sheet of paper

2. _________________________ a brick

3. _________________________ wax paper

4. _________________________ a book

5. _________________________ a window

6. _________________________ plastic wrap

Reflection: bouncing back of a wave when it hits a surface it can’t pass throughMirrors· Mirrors REFLECT light· Types of mirrors· Plane – a flat surface · Concave – surface of mirror curves inward (Make-up Mirror)· Convex – surface of the mirror caves outward (Secruity)

Light usually travels in straight lines called rays. When light rays hit a surface and then bounce off, it is called reflection. You probably see reflection every day. You see it when you look in a mirror.

Light reflects differently off of different surfaces. When light rays hit a smooth surface, they bounce off in the same direction, creating a clear image. When light reflects off a rough surface, it reflects in many directions and does not create a clear image. This is why you can see yourself in smooth surfaces like water but not in rough surfaces like dirt.

The shape of a mirror can affect the way it reflects light. When a mirror is flat, it reflects light rays at the same angle they hit the surface. The image stays the same. If a mirror is curved inward or outward, however, the angle of the rays changes. This causes the image to change too. A mirror whose surface curves outward is a convex mirror. A convex mirror provides a wider field of vision than a flat mirror does, but objects appear farther away. A mirror whose surface curves inward is a concave mirror. The reflection of an object close to a concave mirror is larger than the reflection would be in a flat mirror.

Refraction: the bending of light as it passes through a material with different density

Lenses: REFRACT light· Types of lenses· Concave – thicker at the edges than at the center· Convex – thicker at the center than at the edges

Nearsighted: ability to see close by

· Image forms up in front of the retina so it is corrected

· by spreading the rays out

· You can spread them out using a concave lens

FARSIGHTED: ability to see objects far away

· Image forms up behind the retina so it is corrected by

· making the rays come closer together using a convex lens